Brain Nervous System

The fissure of Rolando is situated about the middle of the outer surface of the hemisphere, and coursing obliquely downward and forward, divides the surface of the hemisphere into approximately equal parts. It commences at or near the longitudinal fissure, a little behind its mid-point, and runs sinously downward and forward, to terminate a little above the horizontal limb of the fissure of Sylvius, and about half an inch of the same fissure. It forms two chief curves; the upper or superior genu in concave forward and upward, while the lower or inferior genu has its concavity directed backward.

The parieto occipital fissure is only seen to a slight extent on the outer surface of the hemisphere; being situated for the most part on its mesial aspect. The portion on the outer surface is called the external parieto pecipital fissure, to distinguish it from the part continued on to the internal surface, which is termed the internal parieto occipital fissure. The external parieto occipital fissure commences about midway between the posterior extremity or occipital pole of the brain and the fissure of Rolando, and runs downward and outward for about an inch.

These three fissure divide the external surface of the hemisphere into four lobes; the frontal, the parietal, the occipital, and the temporal. To this must be added:

1. the central lobe, or island of Reil, which is situated deeply in the Sylvian fissure
2. the olfactory lobe, which is found at the base of the brain and was formerly described under the name of the oflactory nerve.